1. Field of the Invention
The following disclosure relates generally to thermoelectrics configured from heterostructures or thin layers of thermoelectric material to improve performance or usability of such thermoelectrics.
2. Description of the Related Art
The bulk properties of thermoelectric (TE) materials can be altered if the materials are formed from very thin films or segments of alternating materials. The resultant assemblies formed of segments of such thin films are usually called heterostructures. Each film segment is the order of tens to hundreds of angstroms thick. Since each segment is very thin, multiple segments are needed to fabricate cooling, heating and power generating devices. The shape, dimensions and other geometrical characteristics of conventional heterostructures often make attachment of suitable thermal heat transfer members and electrodes to the individual heterostructures assembly difficult. Further complications arise, in the extraction of thermal power from the structures. New fabrication techniques, material combinations, and forming methods are required to fabricate TE elements from such materials. New fabrication techniques are even more critical for systems made from thousands of segments since materials formed of many segments tend to be fragile and weakened by (1) internal stresses that result from fabrication, (2) the very nature of the materials and (3) internal weakness caused by contamination and process variation. Further, certain TE materials, such as those based on Bismuth/Tellurium/Selenium mixtures, are inherently mechanically weak and hence, fragile in heterostructure form.
Heterostructure TE materials generally are configured to be long in one dimension (e.g., wires) or two dimensions (e.g., plates). The TE materials are usually anisotropic with varying thermal, electrical, and mechanical properties along different axes. Electric current either flows parallel to a long dimension or perpendicular to the long dimension(s). In TE elements where the current flows parallel to the long dimension, the length can range up to thousands of times the thickness or diameter of the material. To achieve the desired performance, such TE elements can be made of a multiplicity of heterostructure wires or plates.